This invention relates to a centrifugal actuator for controlling a switch unit and particularly a starting switch unit of an electric motor for disconnecting the start winding when the motor reaches a desired speed.
Centrifugal actuators for motor starting and other applications are well known. A particularly satisfactory centrifugal actuator for AC induction motors is disclosed in U.S. Pat. No. 4,386,290 entitled "Centrifugal Actuator For AC Induction Motors" which issued May 31, 1983 and is assigned to the assignee of the present invention. Generally, known centrifugal actuator units have a common construction consisting of oppositely located and spring loaded levers or arms, each having a general U-shaped configuration. The switching levers have a relatively heavy outer weight connected to the arms which project inwardly from a hinge support member on a base and are interconnected to an axially movable hub member which responds to the pivotal movement of the weight arms. The hub member is aligned with and actuates the switch. The weighted levers respond to the centrifugal forces which rise as the speed of the motor increases. This results in the movement of the switching levers which establish a positive and fast movement of the hub or other switching device which moves relative to the switch. Generally, the force to create the disconnect movement must be somewhat greater than that to maintain the actuator in the run position. Reversely, on deceleration of the motor a return snap action should be created at a designed speed. Generally the cut-out speed and the cut-in speeds will be different. This difference is highly significant in order to conform the switching operation with the pull-up and full load characteristics as well as the break down performance characteristic of the motor.
The centrifugal actuator is required to operate each time the motor is started, slows down or stops. Sliding motions therefor are minimized within the mechanism to reduce wear and to maintain the desired operation. The switch and the interacting switch actuator desirably provides a movement which is not adversely affected over time by any wear characteristic between the switch and the moving part of the actuator. Structures which minimize sliding action and provides pivotal interaction between the parts with minimal wear interaction wherever possible is therefore desired.
Motors can be mounted both horizontally and vertically. A vertically mounted motor is subject to gravitational forces and may effect the operation of the switch actuator if there are significant differences in the hub and the actuating weight structure.
The cost and life of the parts are always of significance in connection with the normal high speed operation of AC motors. Additionally, the pivotal mounting of the weights requires special consideration with respect to maintaining the integrity of the actuator in the event of excessive speed which tend to cause the weights to actually disengage from the switching mechanism.